high speed misfire RGS

andrew112_uk

andrew112_uk

Senior member
Hi everyone,
Been working away at my RGS all winter and it was finally running well  :)  but only for about 100 miles  :(
I'm baffled so maybe this excellent forum can help me. I can run around slowly just fine. But if I take it onto a fast road I get a slight hesitation, just a falter from time to time. This gets worse as the run continues. Stop at the next junction, turn round and all seems well, then I get what feels like the
ignition completely cutting for a second off...then maybe 3 seconds on. It gets worse as the time progresses. But if I leave the fast road and go slowish, all is fine. This did not happen on the early runs and seems to be getting worse.

I thought about fuel starvation and checked the flow from each tap which seems fine and the carb filters are clean. It feels to me like I lose all ignition... not a single cylinder and the loss is not gradual.

A lot of parts have been refurbished so here is a list of usual suspects FYI. All were installed prior to the problem occuring except the coils which I changed yesterday to no effect. New DMC2 setting 7. New plugs, Honda VFR coils, new air filter, rebuilt carbs and new inlet manifolds (keith) valves shimmed. New fuel cap.

Thinking it over, I wonder what is different at higher speed? vibration, heat, timing, generator output all come to mind. I would like to see if I'm actually losing the ignition ...as in maybe the ignition switch cutting out.... but it's hard to check at speed and with quite violent activity in progress. The original wiring is obviously elderly and Italian.

Any thoughts would be much appreciated. I've put a lot of work into my beloved Laverda and I was almost there!
Andrew 
 
  Check the supaseal plug between the optical sensor and the box, these are a right fiddle to put together. I came unstuck with one which demonstrated similar symptoms. The pins in the plug/socket don't always latch first time so pushing the plug together actualy pushes one or more of the pins back out again, causing an intermitant ignition signal.


    Keith.
 
Thanks Keith,

They look OK but it's quite a flimsy connector. Anything to stop me replacing it with a standard set of connectors?

Andrew
 
We chased very similar problems last year on the race bike, re-wired the bike, changed the ignition but the problem still arose. It was finally tracked down by Steve B to an expensive lanyard based kill switch. It definitely sounds electrical and if you have the original wiring then there are a number of places including switchgear where the electrical current could be braking down. On a 120 the handlebars buzz a lot as you pick up speed. If you have some electrical skills, you could try setting up a very simple wiring loom enough to run power to the coils and the ignition, bypassing the original loom then test.
 
I had a very similar problem a while back. After eliminating everything else, I decided it was the DMC 1 playing up. I wrote to Uwe Witt and he sent me a voltage limiter to put in the power supply to the unit. It fixed the problem. Evidently the voltage was going too high. This happened mostly at sustained highway speed when generator output is high. Not a problem when punting around town at lower revs.
(12.5 V was too high for the DMC, Uwe's device drops the supply voltage to 10V).

I don't know whether the DMC 2 has a similar sensitivity to voltage, but it might be worth checking with Uwe.

Since then, my DMC 1 has developed another quirk. It sometimes forgets where the crankshaft is. It keeps making sparks, but the timing is random, so all I get from the engine is pops, bangs, backfires, but no power. Flicking the kill switch off and back on again re-boots the ignition and off it goes again - until the next time it goes haywire. I think it's time to send it to the ignition system retirement home.

Cheers,
Cam
 
Although the DMC connector looked fine, except that the plug takes two ends of standard wire and connects them with tiny pins...  I replaced it with a simple block connector strip. I then took apart the DMC connector and looked in detail but found nothing wrong. My next move was as a post suggested, a wire from the battery to the coil feed to see if that "cured " it. My ignition switch action feels OK and seems to work OK  but it's always moved a little in it's mounting. I did tighten the plastic collar up before I went out to see what difference the DMC block made.

I went out on the same road and did several runs exactly as before and no problems this time. I'm at a bit of a loss to explain that, although I'm very happy. It was a nice ride.

I'm a little suspicious of the ignition switch... wish I had not touched it now. But anyway... no misfire.

I'll post again after a few tests to close the thread and hopefully help anyone with similar problems in future.

Thanks again, Andrew
 
The AMP Superseal connector pins are rated at 14A.  Their size isn't the issue in this application where the optical sensor current is measured in a few mA.  I would strongly recommend that you replace the connector block with something that is waterproof and vibration resistant otherwise over time electrolytic corrosion will see your trigger signal fail or the wires will break under those screws  :(
 
I had a very similar problem with dellorto carbs on a ducati, ran great but when you wound it up it started to missfire.  Check the float bowls for grit, as they engine starts to suck fuel hard they get drawn up into the main jets and it missfires, as you back off the grit falls back into the bottom of the float chamber.
 
Sorry M .. my post was not clear. I meant that my next plan would have been to bypass as much wiring as possible, especially the ignition switch. But the misfire seems to have been cleared by replacing the DMC connection... although I found nothing wrong that I could see. I'm riding it as much as I can and hoping that all is well.
Cheers, Andrew
 
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